The present invention relates to carbon-containing refractories and in particular magnesite-carbon refractory brick suitable for use in metal processing equipment, especially basic oxygen furnaces where high hot strength and high slag resistance of refractory linings are required.
Carbon-containing basic refractory brick have been used in basic oxygen furnaces for many years. In the U.S.A., for example, pitch bonded and burned pitch impregnated magnesite brick have been used since the early 1960's. In other areas of the world, different practices have been used. For instance, pitch bonded and burned pitch impregnated dolomite brick have been used in Europe. In Japan, burned pitch impregnated basic brick with relatively high levels of lime (e.g. 30% CaO and 70% MgO) have been used.
In the late 1970's and early 1980's, a major advance in the technology of BOF refractories was realized with the introduction of magnesite-carbon brick. Unlike the brick that had traditionally been used, this brick contained graphite. Flake graphite was used most often, although in some cases Sri Lankan vein graphite was employed. These magnesite-carbon brick generally had high carbon contents ranging from about 8 to 30%, while the traditional brick contained a maximum of 5% carbon as a rule.
While use of the magnesite-carbon brick in basic oxygen furnaces did result in longer times between furnace relines, it was perceived in early trials that the performance of these brick could be improved by increasing their hot strength and oxidation resistance. As a result, magnesite-carbon brick that contained powdered metals were developed. These brick have been described in U.S. Pat. No. 4,306,030. The metals used in these brick were aluminum, silicon and magnesium. The metals increased oxidation resistance by lowering the permeability of the brick and by consuming oxygen that would otherwise have oxidized carbon. The term "magnesite-carbon brick" as generally used in this industry, and as used herein, refers to brick that contain graphite in combination with deadburned magnesite or magnesia, with the brick containing in excess of 8% by weight carbon.
While the introduction of metal-containing brick represented a significant improvement in BOF refractory technology, it has now become apparent that additional improvements are necessary.